In recent years, procedures have been developed for the transformation of filamentous fungi, including Aspergillus niger, Aspergillus oryzae, and Aspergillus nidulans. U.S. Pat. No. 4,885,249 (Allelix) describes a general process for the transformation of A. niger, exemplified by the introduction of plasmids carrying genes encoding selectable markers.
This method is generally used for the expression and production of proteins originating from other microbial sources, but mammalian proteins have also been produced in such systems.
However, it has been experienced that the expression of trypsins, especially mammalian trypsins only is accomplished to extremely low levels.